1. Technical Field of the Invention
This invention relates to a fastening device for a machine tool such as for the fastening of a milling tool to a milling tool mandrel, or a rotatable carrier for boring or milling machines or the like.
2. Description of the Prior Art
SE,B, 409 832 discloses a device for the fastening of a tool holder wherein an axial screw is tightened rigidly in a bore of the center trunnion of the mandrel. The axial screw has a saucer like head with obliquely arranged lower side and serves as fastener for a tool holder pushed onto and over the trunnion and the axial screw. The device has radially arranged locking screws with conical ends displaceable to engage the obliquely arranged lower side of the head of the axial screw.
The intention behind the known device was to facilitate the changing of tools earlier performed by manipulating a locking screw accessible from the opposite end of the tool holder forcing same into and out from the threaded bore at the mandrel trunnion.
By utilizing a central holding screw having a saucer shaped head with an inwardly inclined inner side, the loosening and fastening operations are facilitated. However, by moving the area of engagement for the locking elements or screws so far away axially from the cooperating axial abutment faces, the stability is endangered. This especially occurs when the tool holder sleeve to be slided onto the mandrel trunnion is too short, as when different makers have different dimensions. The axially acting moment of the inclined surface engaging conical ends of the locking screws will be insufficient to press the sleeve with sufficient force against the abutment face of the mandrel especially when the points of the locking screws meet the axially oriented fastening screw shank. The locating of the locking screws outside the rigid and stable mandrel trunnion might result in heavy wear because of the leverage occurring between the tool holder and mandrel upon operation of the milling tool.